clippard avoid electrical hazards

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FLUID-POWER TECHNOLOGY GUIDE logic can also be used on machines with fluid-power com- ponents but no electrical supply. Air logic does have disadvantages. Most common is a lack of understanding among maintenance personnel on how to read schematics and troubleshoot problems. Also, air logic with long control lines responds notice- ably slower than electronics. That’s because control lines longer than 10 to 15 ft fill and exhaust slowly compared to near-instantaneous electrical signals. In addition, it takes Electrical and electronic devices such as logic circuits, programmable controllers, and PCs normally control fluid-power and fluid-handling circuits. Such systems can also operate with “air logic,” controls that function like relays, switches, time delays, and counters. However, while the circuitry is similar, compressed air is the con- trol medium instead of electric current. Air-logic controls are often preferred in wet or dusty environments because they pose practically no danger of explosion or electrical shock. Likewise, air controls can- not ignite explosive or flammable gases and vapors. And they’re rugged. Water can splash on the controls without affecting operations, and they tolerate dust and dirt. Air Pneumatic controls are a viable option when electrical hazards can’t be tolerated. Authored by: Kenneth J. Korane Managing Editor Key points: • Air logic functions like relays, switches, and counters, but uses compressed air instead of electricity. • Air-logic controls are preferred in wet or dusty conditions because they pose little danger of electrical explosion or shock. Resources: AOP Technologies, www.aoptec.com Clippard Instrument Laboratory, www.clippard.com RS# 621 Magnum Venus Plastech, www.mvpind.com How to … AVOID ELECTRICAL HAZARDS with air logic Air-logic controls for composites manufacturing rely on miniature valves, manifolds, and other components from Clippard Instrument Laboratory. NOVEMBER 8, 2012 MACHINE DESIGN.com 60

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Page 1: Clippard Avoid Electrical Hazards

Fluid-Power Technology guide

logic can also be used on machines with fluid-power com-ponents but no electrical supply.

Air logic does have disadvantages. Most common is a lack of understanding among maintenance personnel on how to read schematics and troubleshoot problems. Also, air logic with long control lines responds notice-ably slower than electronics. That’s because control lines longer than 10 to 15 ft fill and exhaust slowly compared to near-instantaneous electrical signals. In addition, it takes

Electrical and electronic devices such as logic circuits, programmable controllers, and PCs normally control fluid-power and fluid-handling circuits. Such systems can also operate with “air logic,” controls that function like relays, switches, time delays, and counters. However, while the circuitry is similar, compressed air is the con-trol medium instead of electric current.

Air-logic controls are often preferred in wet or dusty environments because they pose practically no danger of explosion or electrical shock. Likewise, air controls can-not ignite explosive or flammable gases and vapors. And they’re rugged. Water can splash on the controls without affecting operations, and they tolerate dust and dirt. Air

Pneumatic controls are a viable option when

electrical hazards can’t be tolerated.

Authored by:

Kenneth J. KoraneManaging Editor

Key points:• Air logic functions like relays, switches, and

counters, but uses compressed air instead of electricity.

• Air-logic controls are preferred in wet or dusty conditions because they pose little danger of electrical explosion or shock.

Resources:AOP Technologies, www.aoptec.com

Clippard Instrument Laboratory, www.clippard.com� RS# 621

Magnum Venus Plastech, www.mvpind.com

How to …

avoidelecTrical hazards with

air logic

Air-logic controls for composites manufacturing rely on miniature valves, manifolds, and other components from Clippard Instrument Laboratory.

NovEMbEr 8, 2012MACHINE Design.com60

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Page 2: Clippard Avoid Electrical Hazards

Fluid-Power Technology guide

much cleaner work environment and reduces the need for protective cloth-ing, respirators, and expensive venti-lation systems. The automated pro-cess also reduces manual labor and improves part quality dramatically.

“Open-molded parts might vary by 15 to 20%, depending on the skill of the operator, and that can gener-ate considerable waste. Closed mold-ing takes that out of the equation by injecting the same amount of resin into the mold every time, resulting in minimal trim waste and less finish-ing after the part is made,” says Aus-tad. Closed molding better controls component thickness and produces a higher-quality part that’s smooth and shiny on both sides, he adds. On open-molded parts, one side usually has a rough, unfinished surface.

But closed molding requires pre-cisely controlled metering and mix-ing of the resin and catalyst, as well as the amount of catalyzed resin in-jected into the mold. While it’s pos-sible to use PLC-based controls with flowmeters, the resins are flammable

a high-quality, filtered air supply to ensure long life.

Air-logic controls are basically miniature three and four-way air valves. Components include the fa-miliar and, or, not, yes, and flip-flop elements, as well as timers and de-lays. Valves provide on or off func-tions like relays or switches, and also exhaust the spent signals. Here’s how one OEM uses air logic to its advantage.

Molding compositesMolded composite parts are com-

monplace in products ranging from boat hulls and hot tubs to storage tanks and wind turbines. However, regulatory pressures are affecting composites-manufacturing pro-cesses, and that has producers turn-ing to pneumatic controls.

“Traditionally, fiberglass and composite parts have been made in an open-molding process,” ex-plains Jeff Austad, vice president of distribution and specialty sales for Magnum Venus Plastech (MVP), a Clearwater, Fla.-based manufac-turer of pumping and meter-mix equipment used to make composites. Typically, workers spray a gel-coated mold with a mixture of catalyzed resin and glass fibers, then the part is oven cured, cooled, and removed from the reusable mold.

Over the last couple of decades, regulations have gotten a lot tougher regarding worker exposure to haz-ardous materials such as styrene, as well as emissions of noxious fumes into the environment, says Austad. Safety concerns have grown, too. The resins are flammable, so minimizing fire hazards and, in turn, insurance costs, are also taking center stage.

That has spurred a move to closed-mold processing. As the name implies, instead of spraying material to make a part, the resin and other constituents are injected into a closed and sealed mold. Versions of this process include resin-transfer mold-ing (RTM), light RTM (vacuum-as-sisted), vacuum-infusion molding, and closed-cavity bag molding.

Closed molding, first of all, lowers emissions, says Austad. It results in a

Pneumatic circuits precisely control resin-injection rate and pressure.

rS# 143

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Page 3: Clippard Avoid Electrical Hazards

Fluid-Power Technology guide

“Customers who require higher precision, say for aircraft or auto-mobile parts held to tight tolerances, are more likely to want this option,” notes Austad. Overpressure can re-sult in parts with inconsistent thick-ness. So sensing pressure lets the con-troller slow the pump, shut off the injector, or both.

The last, and perhaps most im-portant, function is the control in-terlock. At no time can operators ac-cidently push the wrong button and botch the process. During certain cycles, some functions are locked out and not usable. This prevents costly mistakes, says DeLuca.

Precise pumpingPrecise metering was a key objec-

tive when the Patriot was developed. It ensures a catalyst-to-resin variance ratio of 1% or less. A pneumatic mo-tor drives the resin pump which, in turn, is connected by a slave arm to the catalyst pump. In this way, the catalyst pump is directly slaved to the resin pump, ensuring accurate me-tering as both catalyst and resin are delivered to the mix head.

The air motor driving the pumps uses line-pressure pilot valves, which shift a four-way valve spool to reverse the pump. Keys for quickly revers-ing the pump are a light spring load on the pilots and large exhaust ports on the valve. Also, the air cylinder has a 2-in. stroke that minimizes

so that would require explosionproof electrical systems, and they are quite expensive. Instead, MVP’s engineers opted for all-pneumatic controls us-ing valves and logic components from Cincinnati-based Clippard In-strument Laboratory.

Air-logic controlsThe Innovator II control box is an

air-logic panel with no electronics. It is used primarily with MVP’s Pa-triot mix/meter dispensing system, the company’s newest generation of resin-dispense equipment specifi-cally designed for closed molding. This meter-mix system delivers pre-cise quantities of resin and catalyst to the mixing head, blends them, and injects the mixture into the mold.

The pneumatic controls perform three major tasks, explains Tim De-Luca, vice president of MVPs RTM Div. The first is to repetitively inject the same shot size into the cavity ev-ery time, eliminating guess work on the part of the operator. Once user-designated injection parameters are reached, a counter circuit shuts off injection.

Second, the controls manage in-jection pressure and prevent over-pressure conditions which could blow out clamps or resin seals, says DeLuca. A pneumatic switch —called a PV switch — can be mounted in the mold to sense resin pressure for closed-loop control.

Air logic minimizes fire and explosion hazards in composites molding operations.

rS# 145

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Page 4: Clippard Avoid Electrical Hazards

Fluid-Power Technology guide

solvent flush cannot back up into the air supply and ruin the entire controller, thanks to a ‘sacrificial’ blocking valve added to the circuit.

In addition to converting to inch-size fittings and tub-

ing, the plumbing was streamlined and secured with clips for a better appearance and easier troubleshoot-ing. Also, all 70+ lines and valves are labeled for identification versus the schematic.

Finally, the control box can handle remote-control pendant operation, multiple feedback devices, and differ-ent styles of mix-meter equipment.

ensuring reliabilityAlthough the box is designed pri-

marily for the North American mar-ket, MVP’s machines are shipped worldwide. This makes reliability, along with minimal maintenance, es-sential, according to Austad. “From MVP’s standpoint, we have used Clippard products in our pumping systems for many years, with good results,” he says. The design relies on standard components and Clippard has worldwide distribution. “So in case there is a problem, users can go to their local distributor and get it re-paired and up and running as soon as possible.”

“Because of the proven reliability and durability of Clippard air-logic valves, we expect these systems to be trouble-free for many years,” adds DeLuca. “Other than cleaning the air filter, no maintenance is required.” MD

the volume of air that must exhaust when the pump reverses. Older versions used 4 and 6-in. stroke cylin-ders, which take lon-ger to exhaust due to the greater volume of compressed air. All this adds up to faster pumping with quick changes in direction. Low-friction seals, along with a balanced power ratio pneumatic drive, help ensure uniform material delivery at high and low flow rates, says DeLuca.

innovative designThe Innovator II is based on

controls originally built in the United Kingdom for a specific model of MVP’s meter/mix equip-ment. That unit used European-stan-dard components and metric tubing. “We wanted an ‘Americanized’ ver-sion for North America with Clip-pard valves, standard tubing, and other components that are readily available,” says Austad.

And MVP wanted the controls to work with a variety of its equipment. Looking to build greater versatility and functionality into the controls, engineers from MVP and Clippard distributor AOP Technologies, Au-burn, Wash., made key improve-ments, notes DeLuca. “We changed all the control lines to 1/8-in. OD to get faster reaction times on the cir-cuits. All of the valves that actually control outside sources were upsized to allow for more flow so that we could use longer trigger lines outside the box,” he says.

“Using stand-alone brass valves from Clippard, we arranged valves into ‘banks.’ Four of the valve banks are essentially complete circuits, to ease troubleshooting. The fifth is an overall control circuit with flow con-trols for system tuning. Some redun-dancies were removed and common valves were used when possible to re-duce the number of different parts,” notes DeLuca.

Another important feature: the

MVP’s Innovator II controls

are shipped worldwide

and built for durability

and low maintenance.

rS# 147NovEMbEr 8, 2012

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